1. Field of the Art
This invention relates to an ultrasound probe, and more particularly to a multi-plane electronic scan ultrasound probe capable of multi-plane electronic scanning through rotations of an ultrasound transducer.
2. Prior Art
In the field of ultrasound probes which have an ultrasound transducer on a distal end portion of an elongated catheter-like insertion member to be introduced into an internal canal or other intracavitary regions of interest, there have been known in the art the so-called multi-plane electronic scanning type ultrasound probes, for example, as described in Japanese Laid-Open Patent Specification S59-22534. More specifically, as seen in FIG. 1 of the published specification, this prior art ultrasound probe has an ultrasound transducer T mounted on a rotary member R within a dome-like casing D on a distal end section of a catheter member C, the ultrasound transducer T consisting of a large number of piezoelectric ceramic transducer elements P which are arranged in a row on the rotary member R. These transducer elements P are driven successively with a predetermined time lag from one another for an electronic linear or sectoral scan over a certain range through an intracorporeal region to be examined. By turning the rotary member R in the arrowed directions in the drawing, one can obtain tomographic ultrasound images on a number of different scanning lines or planes. For instance, in the case of cardiac ultrasound scanning from the alimentary canal, while holding the distal end portion D of the catheter member C in an opposing position within the alimentary canal, the rotary member R is turned around to make scans from different angles. The multi-plane ultrasound scanning of this sort makes it possible to grip the whole image of the heart, and even to display the image of the heart three-dimensionally after voxel data processing by image processing means.
In this connection, there has been a problem that the catheter member, especially the distal end portion of the catheter member becomes objectionably bulky in diameter when a rotational drive mechanism for the rotary member is incorporated into the casing of the distal end portion to rotate an ultrasound transducer with the rotary member. As a countermeasure for this problem, it has been the general practice to drive the rotary member by remote control from a rotational drive mounted on a manipulating probe head which is connected to the proximal end of the catheter member, transmitting rotation from the rotational drive to the rotary member at the distal end of the catheter member through rotation transmission wires. In this regard, for example, a rotational drive mechanism suitable for the remote control of the rotary member is proposed in Japanese Laid-Open Patent Specification H6-261903. Schematically shown in FIG. 2 is the general layout of the prior art ultrasound probe employing a distal end portion and a manipulating probe head as shown in sections in FIGS. 3 and 4, respectively.
More specifically, indicated at 1 in FIG. 2 is an ultrasound probe itself which is largely constituted by a manipulating probe head 2 and a catheter member 3 which is extended out from the manipulating probe head 2. On the side away from the catheter member 3, a cable 4 is led out from the manipulating probe head 2. The cable 4 is provided with a connector 5 at its proximal end for connection to an ultrasound image observation terminal with a monitor screen. The catheter member 3 has a flexible elongated body 3a of a predetermined length, with an angle section 3b and a distal end section 3b successively connected to the fore end of the flexible body 3a.
As seen in FIG. 3, the distal end section 3c of the catheter member 3 is provided with a casing 10 which internally defines a chamber 10a to accommodate an ultrasound transducer 11. This ultrasound transducer 11 is substantially of the same construction as the one shown in FIG. 1, so that details in this regard are omitted from description and drawings to avoid repetitions. The ultrasound transducer 11 is mounted on a follower pulley 12 which serves as a rotary member. In this case, the ultrasound transducer 11 is mounted on packing material 13 which is fixed on the follower pulley 12. Through an acoustic matching layer 14, an acoustic lens 15 is mounted on a signal transmission and reception face of the ultrasound transducer 11. The acoustic lens 15 is located face to face with an acoustic window 16 which is fixedly provided on the casing 10 of the distal end portion. The chamber 10a of the casing 10 is hermetically closed and filled with an ultrasound transmissive medium like liquid paraffin or the like. Denoted at 18 is a flat cable which is connected to the ultrasound transducer 11.
Along with the packing material 13, acoustic matching layer 14 and acoustic lens 15, the ultrasound transducer 11 constitutes an ultrasound transducer unit 19 which is integrally mounted on the follower pulley 12 so that the transducer is turned about a center point of its active face. Namely, the ultrasound transducer unit 19 is rotatable about an axis which is disposed perpendicularly to the axis of the catheter member 3.
In order to turn the ultrasound transducer unit 19, a pair of rotation transmission wires 20 are lapped in and around an annular groove 12a on the circumference of the follower pulley 12 from opposite directions and securely fixed to the latter at the respective fore ends. On the rear side of the ultrasound transducer unit 19, these rotation transmission wires 20 are led into the angle section 3b via pipes 21 and extended as far as the manipulating probe head 2 through the flexible body 3a. of the catheter member 3. Between the proximal end of the pipe 21 and the manipulating probe head 2, the wires 20 are received in coil sleeves 22 each in the form of a metal wire coil with tightly wound helices. Fore ends of the coil sleeves 22 are connected to the pipes 21 which are fixedly mounted in position within the casing 10, while rear ends of the coil sleeves 22 are securely connected to a rotational drive within a housing of the manipulating probe head 2 as will be described below.
Within the housing of the manipulating probe head 2, the rotation transmission wires 20 which are led out of the coil sleeves 22, as illustrated in FIG. 4, are wrapped in and around an annular groove 23a on the circumference of a drive pulley 23 and securely fixed to the latter at the respective proximal ends. The drive pulley 23 is coupled with an inner end of a rotational shaft 24 the outer end of which is projected out of the housing of the manipulating head assembly 2 and provided with an operating knob 25 to be manipulated by an operator. Therefore, upon turning the knob 25 with fingers, the rotation transmission wires 20 are pulled back and forth in step with rotation of the drive pulley 23, causing the follower pulley 12 to rotate substantially in synchronism with the drive pulley 23. In order to detect the rotational angle of the follower pulley 12, a bevel gear 26 which is provided on the circumference of the drive pulley 23 is meshed with a bevel gear 28 which is in turn coupled with an input shaft 27a of an encoder 27. Therefore, upon turning the drive pulley 23, its rotational angle is detected by the encoder 27 to determine the direction of ultrasound scanning.
By pulling the rotation transmission wires 20 back and forth, the transducer 11 of the ultrasound transducer unit 19 is turned and shifted into a different angular position to make an ultrasound scanning in a different direction or plane. In this regard, since the ultrasound transducer unit 19 is mounted on the follower pulley 12 which has its rotational axis disposed perpendicularly to the axis of the distal end section 3c of the catheter member 3, the direction of an electronic sectoral scanning by the ultrasound transducer 11 lies in a direction perpendicular to the axis of the distal end section 3c. In addition, by bending the angle section 3b which is connected to the distal end section 3c of the catheter member 3, the ultrasound transducer 11 on the distal end section 3c can be turned into an arbitrary direction. Accordingly, through operation of the angle section 3b, the distal end section 3c with the ultrasound transducer 11 can be turned toward a diseased portion or other intracavitary regions of particular interest for ultrasound examination. In case an intracavitary wall to be examined exists at a large angle with the direction of insertion of the catheter member 3, however, there may arise a situation where the operator finds it difficult to locate the ultrasound transducer 11 in an appropriate position in terms of ultrasound scanning range, depending upon positional relations between the path of insertion of the catheter member and the intracavitary region of interest. Besides, although it is desirable for ultrasound signals from the ultrasound transducer to enter an intracavitary wall with an angle of entrance of substantially 90 degrees, difficulties are often experienced in controlling the angle of entrance simply by repositioning the catheter member 3 as a whole or by bending the angle section 3b within an internal canal or the like.